23 Nov
2013
23 Nov
'13
11:44 a.m.
Hi, list!
I want to write function, that will stack `return` as much times, as
necessery. In code, I want
<$> magicLift 2 :: IO Int
<$> magicLift 2 :: Maybe [Int]
both be valid.
My best approach is following (not work)
{-# LANGUAGE FlexibleInstances #-}
{-# LANGUAGE UndecidableInstances #-}
class Monad m => MonadS m where
liftS :: a -> m a
instance (Monad m) => MonadS m where
liftS = return
but
<$> :t liftS 2
liftS 2 :: (Monad m, Num a) => m a
What would you suggest?
--
Best regards, Dmitry Bogatov